Magnetic amplifier



July 15, 19 8 M. MlNTZ ETAL 1 MAGNETIC AMPLIFIER Filed April 13, 1953 FIG. 2

IO SOURCE VOLTAGE FIG.6 FIG.3

MALCOLMF. THOMPSON BY JOHN J. WITTKOPF ATIORNEY MAGNETIC AMPLIFIER Martin Mintz, Long Beach, Gerald D. Shere, Temple City, Malcolm E. Thompson, Bellflower, and John J. Wittkopf, Downey, (Califi, assignors to North American Aviation, Inc.

Application April 13, 1953, Serial No. 348,472

' 14 Claims. (Cl. 32116) This invention relates to magnetic amplifiers, and more particularly to a new magnetic amplifier which is specially suited to operate as apart of a regulated power supply whose output voltage is relatively independent of variations in source voltage or variations in load current.

It a high degree of regulation is desired, methods of regulation such as the use of ballast resistances or constant voltage drop tubes are not satisfactory. Other methods, using several stages of tube amplification become increasingly complex with closer regulation and quite costly if substantial power is required by the load. Associated with the complexity of tube amplified control is the inherent frailty of such amplifiers. The necessary maintenance schedule and regular replacement of parts is a further drawback.

Magnetic amplifier circuitry, therefore, provides advantageous means for controlling the delivery of power from a source to a load. The rugged construction of typical magnetic circuits makes for added reliability; and a remarkable adaptability accounts for increasingly wide application of these circuits. Having no dependence on contacts or moving parts, these devices may be described as static in character, which accounts for their long life with little or no maintenance. Development of high quality core material and low reverse leakage rectifiers have contributed a great deal to the high level of performance now resulting from the use of saturable reactors in magnetic control circuits. T

The present invention is based upon the combined use of saturable reactors and rectifiers, such as diodes, or other means of allowing directional current flow. In functional form, the device may be described as a circuit to reset the flux state of the core of "the saturable reactor, and another circuit to deliver a quantity of power to the load, limited by the previous core reset. Thus, the hysteresis loop of the core material plays a useful part in the operation of the device. Adjustability of the reset circuit provides a control of the amount of power delivered. As in most such instances, both full wave and half wave embodiments are readily devised from the basic scheme. Oftentimes, control windings are incorporated on reactors for additional feedback and control purposes. These may be included in the present case, but are not necessary as will be shown hereinafter. While inclusion of saturable reactors in power supplies for voltage regulation purposes has been proposed heretofore, the magnetic amplifier and the power supply here described are novel. The regulated power supply exhibits an improved time-response characteristic, and is remarkable in its eitectiveness and economy of controlling equipment. This is due, in part, to the simplicity of the magnetic amplifier.

It is therefore an object of this invention to provide a magnetic amplifier having a minimum number of parts.

It is another object of this invention to provide an amplifier that is of simple and rugged construction.

It is another object of this invention to furnish a magnetic amplifier which can be used to control the voltage rates Patent ice delivered to a load despite variations in load current or source voltage.

It is another object of this invention to furnish a magnetic amplifier having high efficiency.

Other objects of invention will become apparent from the following description taken in connection with the accompanying drawings, in which- Fig. l is a schematic of the elementary form of this invention;

Fig. 2 is an idealized hysteresis loop of the core material of the saturable reactor and is included for explanation purposes;

Fig. 3 is a sine wave indicating the source voltage and the voltage and power furnished by the device;

Fig. 4 is a schematic of a full wave application of the device of Fig. 1;

Fig. 5 is a schematic of a voltage regulated power pp y;

And Fig. 6 is a magnetic amplifier incorporating a transistor.

Referring now to Fig. l, 1 denotes a saturable reactor which is series fed by A.-C. source 2. Variable resistor 3 is connected to the other terminal of the A.-C. source 2 and through diode 5 to the reactor 1. Load 4 is connected to the common terminal of resistor 3 and source 2 and through diode 6 to reactor 1. Two paths of current flow are presented, one through variable resistor 3, and the other through load 4. Diode 5 is directed to conduct during one half cycle of A.-C. current flow, and diode 6 is directed to conduct during the other half cycle. Load 4 is any of the typical impedances presented to such power sources and the circuit must, of course, have particular design depending on the requirements of the load. The power delivered from the A.-C. source to the load is controlled by adjustment of variable resistor 3. A signal source E may be substituted for resistor 3 or used in combination therewith. In such an instance, the circuit operates to magnetically amplify the input. Resistor 3 is not, necessarily, matched in size or power dissipation to the load. It may contain reactive impedance. The device operates as follows:

Commencing with the core of the saturable reactor at position 7 on the hysteresis loop of Fig. 2, assume source polarity to be positive so that current next flows through diode 6 and, consequently, load 4. Until the core of saturable reactor 1 reaches point 8, little current flow occurs, and most of the output voltage of the source appears across the winding of the saturable reactor 1. When the core reaches point 8, shown also on the source voltage wave of Fig. 3, the reactor saturates, or fires as it is called, and substantially the entire source voltage appears on the load until the polarity of the source voltage reverses at point 10. During saturation, the core flux density moves to and returns from point 9, on the hysteresis loop, Fig. 2. While the core is at saturation, the winding on the saturable reactor is, effectively, a short circuit, presenting very little impedance to the flow of current and, corresponding therewith, little voltage appears across the saturable reactor. The source voltage must, therefore, appear across the load. Power is then being delivered to the load during the core saturation period which is the cross-hatched portion from point 8 to point 10 on the wave form of Fig. 3.

As the succeeding negative half cycle is produced by the power source, at point 10, core saturation is terminated by reverse current flow through diode 5, variable resistor 3, and the saturable reactor. Power is no longer delivered to the load and the reversed source voltage appears, in the main, across the saturable reactor to demagnetize it. The flux state of the core proceeds from point 10 to point 11, then to point 7, at which time the power source commences a new cycle with the core properly reset for a new cycle. The period 7 to 8 is called firing delay. If firing delay 7 to 8 is short, power delivery 8 to is long. If firing delay 7 to 8 is long, power delivery 8 to 9 to 10 is short. The demagnetizing phase 10 to 7 is called reset. It is apparent that variable resistor 3 determines the amount of demagnetizing current allowed to flow in each negative half cycle and, consequently, determines the reset level of point 7. If resistor 3 is a smaller value, more current is allowed to flow during the core reset phase 10 to 11 (each negative half cycle) and the reset level is that indicated at point 7, Fig. 2. Because the reset value is in a lower excursion, the reactor has a longer firing delay in the next positive half cycle and will not fire as quickly and less power will be delivered to the load. Likewise, if variable resistor 3 is greater, there is less reset current, and the reactor, not being demagnetized so far as previously, will fire earlier in each positive half cycle, and more power will be delivered to the load. The setting of variable resistor 3, or an input signal at that point, therefore, determines, during the negative half cycles, the amount of power to be delivered during the positive half cycles of power input. It accomplishes this result by determining the reset level of the core. It is also apparent that resistor 3 will also determine the average value of the output voltage of the device. It is also noted that the amount of current flow in resistor 3 is small compared to the values of current flowing in the load and, consequently, resistor 3 has considerable resistance and insignificant power dissipation in relation to the load.

The device of Fig. 4 is a full wave extension of the device of Fig. 2. Source 2 is coupled through transformer 12 to saturable reactor 13 which, in turn, is connected through diode 14 to load 15. Load 15 is connected to the center tap of the secondary of transformer 12. Similarly, reactor 18 is connected through diode 19 to load 15. The center tap of the secondary of transformer 12 is connected through variable resistor 15 and diodes 17 and to saturable reactors 18 and 13, respectively. The transformer represented at 12 furnishes power from source 2 during a portion of the positive half cycle through series fed saturable reactor 13, diode 14 to load 15. At this same time, variable resistor 16 and diode 17 are resetting saturable reactor 18. Upon the negative half cycle, power is furnished to load 15 through saturable reactor 18 and diode 19; and variable resistor 16 and diode 21] are resetting saturable reactor 13. Current fiow through variable resistor 16 is always in one direction and, therefore, variable resistor 16 might be replaced by the dynamic plate resistance of a tube, which resistance is controlled by the grid of the tube, or a combination of devices whose effective resistance can be easily controlled. Variable resistance devices such as semiconductors or transistors appear to function favorably as substitutes for variable resistor 16.

Fig. 5 is an embodiment of the full wave principle in a voltage regulator which provides close regulation. Again, A.-C. source 2 is coupled through transformer 12 to saturable reactors 13 and 18. Substituted for the variable resistor 16 in Fig. 4, resistor 21 and the tube 22 connect the center tap of the secondary of transformer 12 through diodes 17 and 20 to saturable reactors 18 and 13. Also, a filter section 23 indicated as having inductance and capacitance, is connected across the output to load 15. A potentiometer Z4 is connected across the output of the filter section. The potentiometer wiper is connected to the grid of tube 22. A voltage regulator tube 25 is connected in series with resistance 21 across the output of the filter section. The power source is shown coupled into a full wave embodiment of the device. The filter section 23 is included to smooth the full-wave rectified output of the saturable reactors and diodes. The variable resistor controlling reset value of each core is the combination of resistor 21 plus the dynamic plate resistance of grid-controlled triode 22. The forward resistance of tube 22 is, of course, determined by the potential of the grid with respect to cathode. Therefore, the power delivered to the load and the magnitude of the smoothed voltage appearing at the load is dependent on the grid to cathode voltage. The grid potential is adjustable by means of potentiometer 24. The cathode potential is stabilized by voltage regulator tube 25.

The feedback inherent in this circuitry holds the de livered voltage to within narrow limits for each setting of potentiometer 24. For example, an increase in supply voltage, whether occurring at the source or resulting from variation in load current, causes an increased peak voltage to be fed to the filter increasing the output voltage of the filter which, in turn, causes the grid of tube 22 to become more positive, which causes the plate resistance of tube 22 to drop. Lowered resistance of tube 22 in the 'eset circuit causes greater reset of the cores, and its resulting reduction of output voltage and power. A decrease in supply voltage would cause a similar stabiliza tion by reducing the core reset levels. This circuit constitutes a voltage regulating closed loop. The result of the closed loop is to reduce the variation in amplitude of output voltage and to maintain the voltage within narrow limits, achieved by the amplification of the tube and the magnetic amplifier itself.

It is apparent that additional control and feedback windings commonly included in saturable reactors may be superimposed on the system, in order to provide regulation of particular characteristics or to provide for further features.

In Fig. 6 is shown a PNP type transistor 26 substituted for variable resistor 16 in Fig. 4. The signal E supplied between emitter and base determines the emitter-tocollector resistance just as in Fig. 5 the grid potential of the tube determines the cathode-to-anode resistance. Rotation of transistor terminals gives slightly different characteristics in the amplifier as does change in type from PNP to NPN transistor.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. In a magnetic amplifier, a saturable reactor, circuit means for allowing current flow in one direction through the load winding of said saturable reactor to a load, reset circuit means for allowing current flow in an opposite direction through said load winding to reset said saturable reactor, and means for controlling the .impedance of said reset circuit means whereby the amount of current flow in said opposite direction is controlled in order to determine the reset level of said saturable reactor.

2. In a magnetic amplifier, a plurality of saturable reactors, circuit means for allowing current flow in one direction through the load winding of said saturable reactors to a load, reset circuit means for allowing current flow in an opposite direction through said load windings to reset said saturable reactors, and means common to the reset current paths of said windings for controlling the impedance of said reset circuit means whereby the amount of current flow in said opposite direction is controlled to determine the reset level of said saturable reactors.

3. In a magnetic power supply, a saturable reactor, a circuit connected to the load winding of said saturable reactor, a first rectifier in the circuit, a load in the circuit, a second circuit connected to the load winding of said saturable reactor, a rectifier in the second circuit disposed to allow current flow in the opposite direction through said saturable reactor from that direction established by the first rectifier and a variable impedance in the second circuit for controlling the current through the load winding of said saturable reactor according to the output voltage of said saturable reactor.

4. In a power supply, an alternating current source, a saturable reactor, a first and second electrical circuit coupling the load winding of said saturable reactor to the alternating current source, a rectifier relatively disposed in each electrical circuit to allow current flow in alternating directions in the load winding of said saturable reactor, a load in one of said electrical circuits, and a variable resistance device in the other of said electrical circuits for controlling the current through said load according to the output voltage of said saturable reactor.

5. In a magnetic amplifier, a plurality of saturable reactors, a load in circuit therewith, means for allowing flow of load current unidirectionally through the load winding of each of said saturable reactors, a variable resistance device in circuit with the load winding of each said saturable reactor, and means for establishing the direction of flow of current through said variable resistor and the load winding of each said saturable reactor in an opposite direction to the flow of load current through the load winding of each said saturable reactor.

6. In a regulated power supply, a power source, a saturable reactor having its load winding connected in series with said power source, a first rectifier in series with the load winding of said saturable reactor, a variable resistance in series with said rectifier and connected at its remote end to the remote end of said power source, a second rectifier in series with the load winding of said saturable reactor, said second rectifier disposed to allow current flow through the load winding of said saturable reactor in an opposite direction from that allowed by said first rectifier, and a load in series with said second rectifier, said load connected at its remote end to the remote end of said power source.

7. In a voltage regulated power supply, a pair of saturable reactors, a power source in circuit with the load windings of said saturable reactors, means for allowing load current flow unidirectionally in the load winding of each said saturable reactor, means for allowing reset current to flow in the opposite direction in the load winding of each said saturable reactor, and means for controlling the flow of reset current in the load windings of saturable reactors according to the output voltage of said saturable reactors.

8. -In combination, a plurality of saturable reactors, means for coupling a power source to the load windings of said saturable reactors, a respective diode in circuit with the load winding of each saturable reactor and said coupling means, means for filtering the output of said saturable reactors and respective diodes, a second respective diode in the circuit with the load winding of each saturable reactor and said coupling means, and means for controlling the flow of current in the second respective diode of each saturable reactor according to the output voltage of the filtering means.

9. The combination recited in claim 8 wherein the means for controlling the flow of current in the second respective diode of each saturable reactor according to the output voltage of the filterin means is a grid controlled tube in circuit with said second respective diodes.

10. In a voltage regulated power supply, an alternating current source, two saturable reactors, a transformer coupling the source to the load windings of said saturable reactors, two diodes each in series with the load winding of its respective sattnable reactor, at filter section connected to the output of the diodes, a potentiometer connected across the output of the filter section, two further diodes each in series with a load winding of a respective saturable reactor, a grid-controlled tube whose plate-to-cathode resistance is in series with said further diodes and the electrical center of the transformer, and a voltage regulator between the cathode of said tube and the output of the filter section.

11. In a magnetic amplifier, an alternating current source, two saturable reactors each of whose load windings is connected in series with a terminal of said source, two diodes each in series with the load winding of a respective saturable reactor, a load connected in series with each diode and the electrical center of said source, two further diodes each in series with the load windings of a respective saturable reactor, a transistor in series with the further diodes and connected to the electrical center of said source.

12. In combination, a plurality of saturable reactors, means for coupling a power source to the load windings of said saturable reactors, a respective diode in the circuit with the load winding of each of said saturable reactors and said coupling means, means for filtering the output of said saturable reactors and respective diodes, a second respective diode in circuit with the load winding of each saturable reactor and said coupling means, and means for controlling the flow of current in the second respective diode of each saturable reactor according to the output voltage of said filtering means, said control means comprising a grid controlled tube in circuit with said second respective diode and means for stabilizing the cathode potential of said tube.

13. In a magnetic amplifier, a pair of saturable reactors, a load, circuit means including an A.-C. power source and said load for providing a unidirectional saturating current flow through the load winding of alternate ones of said reactors on alternate half cycles of said source, a pair of reset circuits each individual to the load winding of one of said reactors for providing a unidirectional reset current flow through each load winding when the other is conducting said saturating current, an electronic Valve having a pair of electrodes connected in common in both said reset circuits, and means for varying the impedance across said electrodes to control the reset current of both said windings.

14. In a magnetic amplifier, a pair of saturable reactors each having a load winding, a load, an A.-C. power source, circuit means coupling said windings, source and load to provide current flow through said load and unidirectionally through alternate ones of said windings on alternate half cycles of said source in a sense to saturate said windings, a pair of reset circuits each individual to one of said windings for providing a unidirectional reset current flow therethrough when the other winding is conducting saturating current, said reset circuits including variable impedance means common to both said reset circuits, and means for controlling the impedance of said common impedance means to control the flow of said reset current through both said windings.

References Cited in the file of this patent UNITED STATES PATENTS 1,920,618 Zierdt Aug. 1, 1933 2,503,880 Mah Apr. 11, 1950 2,653,293 Huge Sept. 22, 1953 2,683,853 Logan May 18, 1956 

